Lamps of the above type are generally classified into two varieties: low-voltage and high-voltage. Low-voltage photoflash lamps typically include a glass envelope with a combustion-supporting gas (e.g., oxygen) and a quantity of filamentary, combustible material (e.g., shredded hafnium or zirconium) therein. A pair of electrically conductive lead wires are usually sealed in one end of the envelope and extend therein. A filament is utilized and interconnects the extending ends of the wires. When the filament is heated by a firing current usually generated from a low-voltage source such as battery or charged capacitor (e.g., having a voltage of from about 1.5 to 15 volts), it ignites a primer material which then ignites the combustible material to produce a flash of light. Naturally, the oxygen gas aids in the above ignition. In high-voltage lamps, the use of a filament is usually excluded by the provision of a glass or ceramic bead in which are located the extending ends of the lamp's conducting wires. The combustible-igniting primer material serves to bridge the portions of these ends which project through the bead. High-voltage lamps also include the aforedescribed filamentary material and combustion-supporting gas. Flashing is accomplished by a firing pulse approaching a few thousand volts and usually provided by a piezoelectric element. In another type of high-voltage lamp, the primer is located within an indentation in the bottom of the lamp and the conductive wires extend therein.
The teachings of the instant invention are particularly concerned with high voltage lamps, although it will be understood from the following that said teachings may be readily extended to lamps of the earlier generation, low voltage variety. Even more particularly, the teachings as provided herein are especially concerned with high voltage lamps wherein the primer material is located in the bottom of the lamp (e.g., along a bottom surface thereof).
Locating the lamp's primer material within a recess, cavity, indentation, etc. at the bottom end (that containing the lamp's two lead-in wires) of the envelope is particularly desirable in photoflash lamps of the subminiature variety (e.g., those having an internal volume of less than about 0.2 cubic centimeters) in view of the relatively large space required for occupancy by the lead-in wires which form part of the lamp's ignition structure (the primer material typically forming the remaining part). While this arrangement allows for the saving of precious internal volume of the lamp's envelope to thereby enable relatively larger volumes of shredded combustible therein, uniform ignition of the combustible shreds can prove somewhat difficult in that the shred mass typically burns from one end of the envelope to the other when ignited. Accordingly, various factors such as extent of compaction and final shred mass location can adversely affect the combustion rate of this mass. This in turn can adversely alter (e.g., extend) the peak output time for the ignited lamp as well as the total light output. With particular regard to peak output time, it is understood that this parameter is critical in view of the requirement that the lamp's peak output must coincide with the shutter operation of the corresponding camera utilizing a photoflash lamp of this variety.
The present invention, as will be defined, describes a photoflash lamp including a novel means of ignition for the lamp's shredded combustible material such that the combustion rate of this material is substantially increased. The invention also enables the shredded combustible material to burn in a substantially more uniform manner than typical photoflash lamps of the prior art. Although the teachings as provided herein are particularly adaptable to photoflash lamps of the electrically-activated, subminiature variety, it is understood that these teachings are also applicable to other varieties of high voltage photoflash lamps, including those containing the aforementioned ignition structure wherein a glass support bead or similar component is also used.
It is believed, therefore, that a photoflash lamp possessing the unique features as stated above would constitute a significant advancement in the art.